1. Field of Invention
This invention relates to vegetation cutting heads; especially for an improved cutting head for a vegetation trimmer.
2. Description of Prior Art
Although several types of vegetation cutting heads are known, there is an existing need for an improved and simplified method of securing a cutting filament line to the cutting head of a vegetation trimmer.
One type of prior art vegetation cutting head utilizes a spool within the cutting head to store cutting filament line which is manually or automatically dispensed as more line is needed during cutting operation. The disadvantages of spool type cutting heads is that they are designed with multiple parts, therefore, becoming expensive to manufacture, complicated to use, as well as having a higher potential for operational failure, examples being U.S. Pat. No. 5,359,777 (Bauer et. al.) and U.S. Pat. No. 4,068,377 (Kimmel et. al.).
Another prior art vegetation cutting head design; the fixed line variety, has negative aspects as well. The current fixed line devices use methods of attachment that involve the weaving of the cutting filament line through various channels, U.S. Pat. No. 4,190,954 (Walto) and U.S. Pat. No. 5,313,770 (Smothers) and U.S. Pat. No. 5,048,278 (Jones) or knotting the cutting filament line for security U.S. Pat. No. 4,644,655 (Boftamiller) and U.S. Pat. No. 5,713,191 (Welton) which uses a slip knot. These methods result in difficulty of removal and reinsertion of the cutting filament line. U.S. Pat. No. 5,303,476 (Tuggle) and U.S. Pat. No. 4,268,964 (Moore) disclosed an efficient vegetation cutting head with ease of removal and securement. These designs, however, have a fixed or removable tabs which have a possibility of mechanical failure; especially from excessive use and wear. U.S. Pat. No. 4,756,146 (Rouse) has a simplified and efficient method of securing the cutting filament line involving guiding the two end pieces of the cutting filament line through channels within the periphery of the disc. However, the manufacturing requires two plates joined into one device to create the channels for the cutting head. This patented invention requires more manufacturing, therefore, more expense. A similar design to the above is U.S. Pat. No. 5,197,264 (Lacey). The Lacey invention is designed as a one-piece, durable, maintenance free vegetation cutting head. Its cutting filament line passage holes are on the periphery of the rim of its disc. However, unlike U.S. Pat. No. 4,756,146 (Rouse), the cutting filament line(s) have to be woven through a series of holes for attachment which creates a time factor for the removal and insertion of new cutting filament line(s).
U.S. Pat. No. 4,571,831 (White III) has independent eyelets which are pressed into slits which impose a slight crimp in the cutting filament line which prevents the cutting filament line from moving. Excessive wear in a short period of time on this multi-piece fixed line vegetation cuffing head would quickly result in mechanical failure.
Another area of limitation in the prior art fixed line trimmer heads is the applicable type and gauge of the cutting filament line material used. Some cutting heads do not allow for substitution of different gauge or type of cutting filament line. An unusual and unique type of vegetation cutting head application is that of U.S. Pat. No. 3,900,071 (Crawford), which is limited to the usage of carpenters nails as cutting elements. A similar type of prior art invention like Crawford's uses nails and string cutting filament to achieve it's cutting ability is U.S. Pat. No. 5,493,785 (Lawrence). Both the Crawford and Lawrence inventions prove effective for cutting heavy vegetation. Unfortunately, they are somewhat dangerous if mechanical failure of the vegetation cutting head were to occur while in operation during high revolutions.
There are cutting heads that vary from one to six strands of cutting filament line, as well as a type that incorporates string cutting filament line with a cutting blade in unison, U.S. Pat. No. 4,513,563 (Roser). This invention would require more maintenance and expense in replacement of both types of cutting filament lines.
The earlier vegetation cutting heads of one and two strand cutting filament line(s) are being improved by four to six strand types which give better cutting ability and longevity of string cutting filament.
A recent patent, U.S. Pat. No. 5,479,763 (Coble) has overcome part of the deficiencies of the previous fixed line cutting heads. However, Coble still hasn't conquered the two types of stresses on the cutting filament line. Due to the perpendicular placement of the cutting filament line passages, the cutting filament line is forced to bend at nearly a ninety degree angle due to rotational force under high speed revolutions of the vegetation cutting head as well as centrifugal force making the cutting filament line(s) project outwardly. This causes the heaviest stress point at the bend of the cutting filament line and causes premature wearing and/or breaking of the cutting filament line at this point. Coble criticizes the Lacey invention stating that the cutting filament line orientated outwardly have a tendency to break. Experimentation has demonstrated that Coble's criticism is incorrect. As the outward angle of the passage holes is increased, the cutting filament line has to bend less; therefore, resulting in less breakage.
Another problem with Coble's invention is slippage of the cutting filament line due to the parallel placement of the cutting filament line passage holes to the circumference of the disc. The placement doesn't allow the cutting filament line to equally rest on the disc between the plurality of holes, but instead, causes unequal stress due to the trailing effect on the cutting filament line which results from the rotational force and centrifugal force combined.
The present invention overcomes all of the disadvantages of the prior art vegetation cutting heads above and fulfills an existing need for an improved and simplified method of securing a cutting filament line to the cutting head of a vegetation trimmer.